H. DAVID PIXLER
APLNET - A LOCAL AREA COMPUTER NETWORK
APLnet is a high data rate system developed at APL to interconnect dissimilar computers in order
to share computer resources and functions. It can be expanded to include additional computers from
a variety of vendors .
BACKGROUND
Modern computer systems such as the IBM 3033,
VAX-I1, and CRA Y-1 internally perform significant
numbers of reliable data transfers and data manipulations. However, when data must be transferred at
high rates between dissimilar computers or when the
distance is greater than 200 feet between similar equipment, special hardware and software are required.
In the past, data communication between dissimilar computer architectures has required computer links
that were both very expensive and technically difficult
to implement and use. These systems were usually one
of a kind, with many operational and maintenance
limitations.
When either of the linked computers was modified
or enhanced or a new release of software was installed,
additional changes were usually required in the communications system, with an associated downtime to
deal with the problems. If either computer is replaced
(even with the same manufacturer's equipment), the
communications link usually also needs to be q::placed
beca~se of subtle differences between the hardware
and s'o ftware of the computer technologies erpployed
and the design of later-generation equipment. This
would include both hardware interfaces and the communications software.
The F. T. McClure Computing Center at APL, in
conjunction with several other APL technical groups,
has been studying the development of wide-bandwidth
data communications for computers. A general-purpose computer networking technology is now available
so that heterogeneous networks are a practical option.
taining up to a million bytes per frame) need to be
viewed, processed, and/ or printed on film or paper.
In the past, these data from the IBM 3033 were stored
on a magnetic tape and hand carried to another building for viewing, printing, and processing.
Resource sharing has become one of the main advantages of a computer network. Expensive and
sophisticated peripherals need not be duplicated on
each computer. With a network, the peripherals are
available to all users of the network.
WHAT IS APLNET?
A network task force team was formed in 1980 to
study, plan, and implement a general-purpose widebandwidth data communications system for the sharing of computer resources. Many types of computer
networking architectures and systems designs were
evaluated for use at APL. The results of these studies
-the design goals-used in the development of a local area computer network are listed in Table 1. The
boxed insert shows the components of the network that
have evolved as APLnet.
Table 1-APLnet design goals.
The APLnet network was designed to
• Interconnect computers of various manufacturers, initially Digital Equipment Corp. and IBM
• Have high intercomputer data rates (up to 50 megabytes
per second)
• Build on commercially available hardware and software
WHY A NETWORK?
With increasing frequency, APL is engaged in projects for which distributed computing is a necessity.
In the past, the transfer of data from one computer
to another was an awkward process involving either
the physical transport of magnetic tapes or the use of
modems and low-speed telephone communications
lines.
Applications that use distributed computing include
image processing and the formatting and processing
of large databases. An example of this work is the
processing that involves the creation and manipulation
of graphic images on the IBM 3033. The images (con284
• Have high intercomputer communication data rates over
distances up to 5000 feet
• Have expansion capability
• Provide user-friendly software protocols
The implementation of a unified Laboratory-wide
local network for interconnecting computers, with
well-defined and consistent user interfaces, has made
distributed processing applications easier to implement, faster, and more interactive. In addition, a network makes feasible new applications and the sharing
Johns Hopkin s A PL Technical Digest
APLNET COMPONENTS
HYPERcbannel. Hardware to interconnect dissimilar computers. A
high-speed 50 megabytes per second
serial " bus " with intelligent node interface adapters , manufactured by
Network Systems Corp. Almost any
computer can be connected to the network adapters through its standard input/output interfaces or channels. The
adapters manage the flow of data to
and from the attached computers and
include a microcomputer that manages
the buffering and formatting required
on HYPERchannel.
NETEX software. Designed to
connect the HYPERchannel adapter
to the associated computer's operating system and to provide a user interface. Netex, developed by Network
Systems Corp. and available for most
popular computers , provides singlevendor support for both hardware and
software.
APLnet. The combination of equipment supplied by Network Systems
Corp. and the APL-developed utilities
and application programs that do the intercomputer communications and the
data-conversion routines, and make the
system convenient and easy to use.
~
A
HYPE Rchannel trunk
~
I Adapter I
I Adapter I
I Adapter J
I adapter
Link I
Adapter
v
~ telephone
Microwave or
communicati on
link to
Baltimore or
other remote
locations
IBM 3033
(F. T. McClure
Computing
Center)
DEC PDP-11/70
(F . T. McClure
Computing
Center)
VAX-11/750
(Combat Systems
Evaluation
Laboratory)
VAX-11/750
(Combat Systems
Evaluation
Laboratory)
I Adapter I
I
ETHERNET coaxial cable
ITerminal
I·
• • •
• •ETHERNET
I adapter
Link I
Future
computer
•
~ TerminalJ
I
Terminal
Device
I
Computer
at The Johns
Hopkins University
main campus
in Baltimore
Figure 1-The block diagram of the current configuration of APLnet hardware is shown in black; the red sections illustrate
how APLnet may be expanded . The portion in light red is a diagram of how this network may be expanded to include additional computers and access to ETH ERN ET devices at APL and to computers at remote locations. Although the equipment
in the dark red box illustrates a link to The Johns Hopkins University campus in Baltimore, the link could be to any place
in the world with the appropriate microwave , telephone , or satellite communications .
of expensive peripheral equipment among various
computer systems. Data conversion routines are
provided that allow the translation and conversion of
numbers or characters to the format needed for each
computer.
The black portion of Fig. I is a block diagram of
the current configuration of APLnet hardware, which
connects computers in three different buildings via a
1200 foot coaxial cable.
APLnet is used daily to transfer data from the IBM
3033 to the PDP-1l / 70, which is in a separate building, for processing and use of the special peripherals
Volume 5, Number 3, 1984
such as the Dicomed color film recorder and the
multiple-pen CalComp drum plotter. The PDP-1l / 70
and VAX-II also use the network-moving files between the systems-and such resources of the IBM
3033 as the laser printer.
With the advent of the ETHERNET network on the
VAX-II, the APLnet will have additional resources
available. Another natural expansion of the network
would be to provide a remote link to The Johns Hopkins University. This could be implemented by means
of a microwave link or high-speed telephone lines, as
shown in Fig. 1.
285